Soft contact lenses are a representative example of commercial soft ophthalmic lenses. A hydrogel material having a water content of about 25% to about 80% is generally used for commercial soft contact lenses. However, because a hydrous soft contact lens formed of the hydrogel material contains water, a phenomenon in which water vaporizes from the contact lens occurs. This caused a certain percentage of contact lens wearers to have a stronger dry feeling than with the naked eyes and feel uncomfortable. Some complained of a symptom called contact lens dry eye. The hydrous soft contact lens formed of the hydrogel material is likely to be contaminated with some components within lacrimal fluid, and has a risk of growth of bacteria because it contains a large amount of water.
A known example of highly oxygen permeable low hydrous soft contact lenses is a silicone rubber lens obtained by a method including adding a platinum catalyst to a mixture of polydimethylsiloxane with both ends of its molecular chain capped with vinyl methyl silyl groups and methyl hydrogen polysiloxane and heat curing the mixture by molding (see Patent Literature 1).
Described in Patent Literatures 2 to 6 and the like are contact lens materials having high oxygen permeability mainly consisting of polysiloxane having a plurality of polymerizable functional groups. Among them, disclosed in Patent Literature 6 is a contact lens material formed of a polymer obtained from a bifunctional organic siloxane macromer alone or obtained by copolymerizing the macromer with another monomer. Disclosed monomers for use in the copolymerization are acrylic acid fluoroalkyl esters or methacrylic acid fluoroalkyl esters and acrylic acid alkyl esters or methacrylic acid alkyl esters.
However, the conventional highly oxygen permeable low hydrous soft contact lenses have the following problems. First, the silicone rubber lens has failed to achieve wide practical, use owing to drawbacks including the peeling off of a hydrophilization-treated layer formed in order to improve the hydrophobicity of the lens surface and the occurrence of adhesion onto a cornea resulting from its too much elasticity.
The material mainly consisting of polysiloxane having a plurality of polymerizable functional groups is, having high oxygen permeability and also flexibility, considered as one of the materials suitable for contact lenses. However, adhesiveness remains on the lens surface after polymerization, which may cause adhesion of the lens to a cornea, and is unsatisfactory in the balance of flexibility and mechanical properties such as resistance to bending as a lens.
Various methods are known for modifying the surface of soft ophthalmic lenses, and known among them is a method including applying layers of two or more kinds of polymer materials one layer after another and stacking them (e.g., see Patent Literatures 7 to 9). Among them, a method that applies polymer materials having opposite electric charges alternately one layer after another is called the LbL method or the like, in which it is considered that the layers of one material are noncovalently bonded to the other layers of the different material. However, the highly oxygen permeable soft ophthalmic lens that clearly demonstrates the usefulness of that method is only those having a silicone hydrogel material, and the usefulness with respect to the low hydrous soft ophthalmic lenses has not been known. Conventional LbL coating has been performed with multiple layers including about 4 to 20 layers, which might make a manufacturing process longer and cause an increase in manufacturing costs.
With respect to another method for modifying the surface of ophthalmic lenses, Patent Literature 10 discloses irradiating a lens with a specific ethylene oxide derivative brought into contact therewith with radiation to fix the ethylene oxide derivative onto the lens surface. Patent Literature 11 discloses immersing an ophthalmic lens into a solution of a hydrophilic compound containing a water-soluble peroxide and gives rise to graft copolymerization. Patent Literature 12 discloses immersing a hydrogel base material into a solution of a macromolecular compound and irradiating the hydrogel base material with gamma rays.
However, none of these pieces of Patent Literature 10 to 12 discloses surface treatment for reducing or avoiding a phenomenon of sticking of the lens to a cornea when worn.
Patent Literature 13 discloses a method for manufacturing a soft ophthalmic lens in which a layer formed of an acidic polymer and a basic polymer (hereinafter, a coating layer) is formed on at least part of the surface of a base material for a soft ophthalmic lens, thereby remarkably reducing or avoiding a phenomenon of sticking of the lens to a cornea when worn and achieving to manufacture the lens by a simple process and economically.
However, for two-week wearing or one-month wearing disposable ophthalmic lenses, the performance of the coating layer may decrease when worn or when rubbing the ophthalmic lens for cleaning, the method needs improvement.